feat: add treefmt-and-git-hooks template

[sei40kr]

Summary

• Add a new template treefmt-and-git-hooks that sets up treefmt and git-hooks.nix with blueprint
• Includes formatter configuration with nixfmt
• Pre-commit hooks for nil, statix, and treefmt

Template structure

templates/treefmt-and-git-hooks/
├── .envrc
├── .gitignore
├── flake.nix
└── nix/
    ├── checks/
    │   └── pre-commit-check.nix
    ├── devshell.nix
    ├── formatter.nix
    └── treefmt.nix